LM3S3748 Datasheet, PDF (45/753 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S3748 Microcontroller
2.2.6
2.2.6.1
2.2.6.2
Nested Vectored Interrupt Controller (NVIC)
The Nested Vectored Interrupt Controller (NVIC):
■ Facilitates low-latency exception and interrupt handling
■ Controls power management
■ Implements system control registers
The NVIC supports up to 240 dynamically reprioritizable interrupts each with up to 256 levels of
priority. The NVIC and the processor core interface are closely coupled, which enables low latency
interrupt processing and efficient processing of late arriving interrupts. The NVIC maintains knowledge
of the stacked (nested) interrupts to enable tail-chaining of interrupts.
You can only fully access the NVIC from privileged mode, but you can pend interrupts in user-mode
if you enable the Configuration Control Register (see the ARM® Cortex™-M3 Technical Reference
Manual). Any other user-mode access causes a bus fault.
All NVIC registers are accessible using byte, halfword, and word unless otherwise stated.
Interrupts
The ARM® Cortex™-M3 Technical Reference Manual describes the maximum number of interrupts
and interrupt priorities. The LM3S3748 microcontroller supports 37 interrupts with eight priority
levels.
In addition to the peripheral interrupts, the system also provides for a non-maskable interrupt. The
NMI is generally used in safety critical applications where the immediate execution of an interrupt
handler is required. The NMI signal is available as an external signal so that it may be generated
by external circuitry The NMI is also used internally as part of the main oscillator verification circuitry.
More information on the non-maskable interrupt is located in “Non-Maskable Interrupt” on page 69.
System Timer (SysTick)
Cortex-M3 includes an integrated system timer, SysTick. SysTick provides a simple, 24-bit
clear-on-write, decrementing, wrap-on-zero counter with a flexible control mechanism. The counter
can be used in several different ways, for example:
■ An RTOS tick timer which fires at a programmable rate (for example, 100 Hz) and invokes a
SysTick routine.
■ A high-speed alarm timer using the system clock.
■ A variable rate alarm or signal timer—the duration is range-dependent on the reference clock
used and the dynamic range of the counter.
■ A simple counter. Software can use this to measure time to completion and time used.
■ An internal clock source control based on missing/meeting durations. The COUNTFLAG bit-field
in the control and status register can be used to determine if an action completed within a set
duration, as part of a dynamic clock management control loop.
Functional Description
The timer consists of three registers:
April 08, 2008
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Preliminary